This invention pertains to a method and apparatus for contact winding wherein a lay-on roll exerts a nip force against a roll of film winding upon a core and, in particular, wherein the lay-on roll moves away from the center of the core during winding along a straight path colinear with a line connecting the center of the lay-on roll and the center of the core while maintaining a substantially constant nip force.
Apparatus for winding a thin web of material, such as paper or plastic film, in roll form on a cylindrical core is essential for the production and handling of a film web. It is especially desirable to maintain uniform pressure between the core of a windup roll and an adjacent lay-on roll for compressing film thereon in the case where a thin web of a resilient and deformable material, such as a plastic film, is to be wound. Pressure variation during winding must be minimized to ensure a uniform winding of successive layers and to obtain high quality roll formation.
U.S. Pat. No. 2,620,993 discloses apparatus appropriate for automatic web winding including a mechanism for severing a continuous web from a completed roll and transferring the severed end to an empty core of another roll. This winding apparatus has a plurality of positions for holding a winding core on the frame so that the winding of the web can be effected continuously and automatically, allowing the removal of a finished roll to take place at one position while enabling web winding to continue in another. As the web is wound onto the winding core, the core position is held stationary and a lay-on roll is held in contact with the winding roll over the complete working width at a prescribed pressure at the nip, i.e., the area of contact between the rolls. The optimum value for the pressure applied by the lay-on roll during winding is established experimentally and includes factors such as the material width as well as the mechanical properties of the film at the desired film thickness.
U.S. Pat. No. 4,850,545 discloses an apparatus for maintaining lay-on roll pressure on a winding core while a roll of film is being wound. This reference provides two means for controlling the pressure applied by the lay-on roll to the roll of the film: airsprings pivotally rotate bellcranks holding the lay-on roll to maintain fine control of the loading pressure while piston-cylinder assemblies, synchronized by a connecting shaft, horizontally index the pedestal arms mounted to the lay-on roll bellcrank assembly as the roll increases in diameter.